For many years it has been known to drill horizontally through a pay zone in order to expose a large area of the production formation to the wellbore and thereby vastly increase the production rate of the well. It is known to slant a borehole by using a whip-stock in order to offset the well using a conventional drill string; however, it is difficult to enter a thin hydrocarbon bearing formation using this technique.
It is desirable to be able to drill a lateral from a vertical borehole at a precise location that assures the lateral penetrating the production formation. This is difficult to achieve, especially with thin or irregular formations.
Accordingly, after a well has been geologized, and the payzone precisely located, the formation of a lateral borehole that extends from the vertical at the precise location required to intercept and penetrate the payzone is more likely to be made possible if an unusually small radius of curvature can be effected into the drill string and casing.
Method and apparatus for achieving the above desirable goals is believed to be possible by the provision of a flexible drill string that does not require a downhole motor driven bit; that can make a sharp bend to turn the borehole laterally and thereafter continue to drill while being rotated by a rotary turn table of a drilling rig; and such a method and apparatus is the subject of the present invention.